Laser photochemistry of oxygen. Application to studies of the absorption spectra of dissolved oxygen molecules

This paper summarizes the data of our lab on the rates of photooxygenation of singlet oxygen traps upon direct laser excitation of oxygen in air-saturated organic solvents and water. Methods of application of these data to calculation of absorbance (A) and molar absorption coefficients (ε) in the maxima of the main oxygen absorption bands (1273, 765 and 1070 nm) are discussed. The most accurate results were obtained from comparing the photooxygenation rates upon porphyrin-photosensitized and direct excitation of oxygen molecules. It is shown that ε1273 is not sensitive to the presence of heavy atom (bromine) in solvent molecules and markedly decreases on going from non-polar solvents to water being proportional to the radiative rate constants obtained from the quantum yields of singlet oxygen phosphorescence at 1274 nm. The coefficient ε765 markedly increases in the presence of bromine. In solvents lacking heavy atoms the 1.5-2-fold increase of ε765 was observed on going from non-polar solvents to water. Simultaneously, the ratios ε1273/ε765 are changed from (7-10)/1 in non-polar solvents to 1.5/1 in water. The value of ε1070 obtained in carbon tetrachloride is shown to be about two orders smaller than ε1273 in the same solvent. The results are important for both analyses of oxygen photonics and dosimetry of laser radiation in biomedical experiments.